The development and utilization of home testing has revolutionized the management of chronic diseases such as diabetes mellitus. We propose here a plan to develop a home test kit for analytes such as ammonia and amino acids that would revolutionize the management of aminoacidopathies, urea cycle disorders, and other inborn errors of metabolism. These diseases (for example, PKU) require complex testing for diagnosis and clinical monitoring. While uncommon, individuals suffering from these disorders consume significant amounts of expensive medical care. Treatment requires frequent monitoring of serum amino acid levels, and in the case of the urea cycle disorders, ammonia, to avoid significant morbidity and mortality. In fact the recent NIH consensus statement for PKU stated, "Development of a reliable home-testing method is recommended, as well as measures to increase adherence." In order to improve the care of patients with these inborn errors of metabolism, we will develop photonic crystal sensors for ammonia and specific amino acids that patients could use for home monitoring. Our objective is to develop a sensing materials that can be incorporated into a device that utilizes a small amount of blood from a fingerstick. The blood would be placed on a photonic crystal film sensor that would rapidly change color in response to the concentration of a particular amino acid and/or NH4*. The analyte sensing will be monitored by using a simple Palm Pilot-type instrument that utilizes a color CCD camera. The results could be immediately displayed, and easily recorded if the device is operated as a patient biographer.